As the Ethernet develops towards multi-service bearer, especially some services become increasingly demanding on reliability and real-time performance of the network, the Ethernet employs a ring networking structure to improve the reliability of the network. In a protection method of the ring network, fast protection switching is usually required, and it is also required that the time for protection switching is less than 50 ms. At present, as to the fast protection switching technology, there are RFC3619 of the Internet Engineering Task Force (referred to as IETF), G.8032v1 of the International Telecommunication Union (referred to as ITU-T), and so on.
FIG. 1 is a topological diagram of the Ethernet ring network according to the related art. As shown in FIG. 1, nodes A to F are nodes having a Ethernet switching function, a network M is connected with the node B, and a network N is connected with the node D. There are two physical paths between the network M and the network N, viz.
network Nnode Dnode Cnode Bnetwork M; and
network Nnode Dnode Enode Fnode Anode Bnetwork M.
When the Ethernet ring protection technology is applied, a ring protection link and a control node are defined, viz. in the case that there is no failure in the Ethernet ring network, a link in the Ethernet ring network which blocks data messages to prevent the formation of a loop is a ring protection link. The switching between a primary path and a protection path of the Ethernet ring network can be carried out by performing operation on this ring protection link, wherein a node owning the ring protection link is referred to as a control node (or referred to as a master node).
FIG. 2a is a topological diagram of the communication path when the links in the Ethernet ring network are in good condition in the prior art. As shown in FIG. 2a, the nodes included in the Ethernet ring network are nodes A, B, C, D, E and F, and the links included in the Ethernet ring network are links <A,B>, <B,C>, <C,D>, <D,E>, <E,F> and <F,A>, wherein the node A is the control node, and the link <F,A> directly connected to a port a2 is the ring protection link.
When the links in the Ethernet ring network are in good condition, the control node blocks a data message forwarding function of the port connected to the ring protection link, and no loop is generated in the network, which avoids “broadcast storm” caused by a network loop. As shown in FIG. 2a, the control node A blocks the data message forwarding function of the port a2, and the communication path between the network M and the network N is: network Mnode Bnode Cnode Dnetwork N.
When a failure occurs in a link in the Ethernet ring network, the control node opens the data message forwarding function of the port at which the control node is connected with the ring protection link, which ensures the connectivity of the service. As shown in FIG. 2b, a failure occurs in the link <B,C> in the Ethernet ring network, the control node A releases the data message forwarding function of the port a2, and the new communication path between the network M and the network N is: network Mnode Bnode Anode Fnode Enode Dnetwork N.
When a link switching occurs in the Ethernet ring network (for example, a failure occurs in a link or the failure disappears), it is required to refresh an address forwarding table. The refreshing of the address forwarding table serves to prevent the nodes from using the path before the link switching to forward data messages, so as to avoid great loss of the data messages. As shown in FIG. 2a, in the case that there is no failure in the links in the Ethernet ring network, the path through which the network N transmits a data message to the network M is: network N→node D→node C→node B→network M. FIG. 2b is a topological diagram of the communication path when a failure occurs in a link in the Ethernet ring network in the prior art. As shown in FIG. 2b, when a failure occurs in the link <B,C>, if the forwarding table of the node D is not refreshed, the transmission of the data messages from the network N to the network M is still performed along the original path, these data messages are discarded at the node C, and this phenomenon continues until the node D learns the correct address of the node B. Thus, in the G.8032v1, it is the general practice to use the method of refreshing an address forwarding table to prevent the nodes from still using the path before the link switching to forward data messages.
In the G.8032v1, address refreshing information is usually indicated by a DNF field of a link failure notification (Signal Fail, referred to as SF) protocol message and of a No Request (referred to as NR) protocol message. These protocol messages are usually periodically transmitted by a source node, so that the Ethernet ring network is stable in one state. In the G.8032v1, a node only has an idle (IDLE) state and a protection (PROTECTION) state, which are respectively defined as follows.
IDLE state: there is no failure in the Ethernet ring network, the No Request-Ring Protection Link Blocked (referred to as NR-RB) protocol message periodically transmitted by the control node indicates that the ring protection link has blocked the forwarding of the data messages; and the nodes in the Ethernet ring network all enters the IDLE state after receiving the protocol message.
PROTECTION state: there is a failure in the Ethernet ring network, the node which detects the failure periodically transmits an SF protocol message; and the nodes in the Ethernet ring network which receive the SF protocol message enter the PROTECTION state.
In order to prevent the nodes from repeatedly refreshing the address forwarding table, in the G.8032v1, it is agreed that, a node refreshes the address forwarding table only once in one node state. FIG. 3a is a schematic diagram of the transmission of the SF protocol message when a failure occurs in a link in the Ethernet ring network in the prior art. As shown in FIG. 3a, a failure occurs in the link <B,C> in the Ethernet ring network, the node B and the node C periodically transmit outwards the SF protocol messages along the port b2 and the port c1, respectively. Although the nodes D, E, F and A in the Ethernet ring network can constantly receive the SF protocol message, these nodes refresh the address forwarding table only once in the PROTECTION state, viz. the nodes refresh the address forwarding table when receiving the first SF protocol message in the PROTECTION state, and ignore the SF protocol messages received subsequently.
The above address refreshing mechanism (viz. the address forwarding table is refreshed only once in one state and the nodes only have two states, viz. the IDLE state and the PROTECTION state) operates properly under an inversion recovery mode, but malfunctions under a non-inversion recovery mode.
The inversion recovery mode indicates: when the failed link in the Ethernet ring network returns to normal, the forwarding of the data messages is blocked only at the port where the control node is connected to the ring protection link in the entire Ethernet ring network. The non-inversion recovery mode indicates: when the failed link in the Ethernet ring network returns to normal, for the entire Ethernet ring network, the port at which the forwarding of the data messages is blocked is not necessarily the port where the control node is connected to the ring protection link.
Under the inversion recovery mode, when the failure of the link <B,C> in the Ethernet ring network disappears, the nodes B and C periodically transmit outwards the NR protocol message along the port b2 and port c1, respectively, for indicating that the failure of the link disappears; after receiving the NR protocol message, the node A starts a timer, blocks data message forwarding function of the port a2 after the timer expires, and transmits an NR-RB protocol message; after receiving the NR-RB protocol message, each node in the Ethernet ring network enters the IDLE state, and refreshes the address forwarding table in accordance with the DNF field of the NR-RB protocol message.
However, under the non-inversion recovery mode, as shown in FIG. 3b, FIG. 3b is a schematic diagram of the non-inversion recovery of the Ethernet ring network in the prior art, when the failure of the link <B,C> in the Ethernet ring network disappears, the nodes B and C periodically transmit outwards an NR (NODE_ID) protocol message along the port b2 and port c1, respectively; when receiving the NR (NODE_ID) protocol message transmitted by the node C, the node B finds that the NODE_ID (node identifier) of the node C is greater than the NODE_ID of the node B, then, the node B stops transmitting the NR (NODE_ID) protocol message, and at the same time, opens the data message forwarding function of the port b1; the node C keeps blocking the data message forwarding function of the port c2. According to the provisions of node state in the G.8032v1, at this time, each node in the Ethernet ring network is still in the PROTECTION state, and will not refresh the address forwarding table. In this case, if a new failure occurs in the links in the Ethernet ring network at a later time, there will be a problem in the address refreshing of the node. FIG. 3c is a schematic diagram of the case that, after one link in the Ethernet ring network is performed with the non-inversion recovery, a failure occurs in another link in the prior art. As shown in FIG. 3c, after a period of time since the failure of the link <B,C> disappears, a failure occurs in the link <E,D> of the Ethernet ring network, the node E and the node D, after detecting the failure, periodically transmit outwards the SF protocol message along the port e2 and port d2, respectively, and after receiving the SF protocol message, the node C opens the data message forwarding function of the port c2. Since each node in the Ethernet ring network is still in the PROTECTION state at this time, none of the nodes will refresh the address forwarding table. However, as new changes have taken place in the topological structure of the Ethernet ring network, if the nodes in the Ethernet ring network do not refresh the address forwarding table, the data flow in the Ethernet ring network will be forwarded along the original path, viz. the path before changes have taken place in the topological structure of the Ethernet ring network (i.e. node Bnode Anode Fnode Enode D), and there will be a great loss of data.
From the above analysis, the use of the address refreshing method in the prior art under the non-inversion recovery mode will lead to data loss due to the failure in refreshing the address in time.